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Trimerophytopsida; Temporal range: Devonian PreꞒ Ꞓ O S D C P T J K Pg N
	Fossil of Psilophyton dawsonii
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Class:	†Trimerophytopsida; A.S.Foster & E.M.Gifford 1974
Order
	†Trimerophytales
Synonyms[citation needed]
	Trimerophyta (orth. var.); Psilophyta (orth. var.); Trimerophytophyta Bold 1973; Trimerophytophytina Banks 1975; Psilophytophyta Zimmermann 1930; Psilophytophytina Kryshtofovich 1945;

Trimerophytopsida (or Trimeropsida) is a class of early vascular plants from the Devonian, informally called trimerophytes. It contains genera such as Psilophyton. This group is probably paraphyletic, and is believed to be the ancestral group from which both the ferns and seed plants evolved. Different authors have treated the group at different taxonomic ranks using the names Trimerophyta, Trimerophytophyta, Trimerophytina, Trimerophytophytina and Trimerophytales.

Taxonomy

At first most of the early land plants other than the bryophytes (i.e. the polysporangiophytes) were placed in a single class Psilophyta, established in 1917 by Kidston and Lang.^[1] As additional fossils were discovered and described, it became apparent that the Psilophyta were not a homogeneous group of plants. In 1968 Banks first proposed splitting this taxon into three groups, which he put at the rank of subdivision; he clarified his proposal in 1975. One of the three groups was the Trimerophytina.^[2]^[3] The subdivision is based on the type genus Trimerophyton, which might be expected to produce 'Trimerophytophytina' as the name of the subdivision, but the International Code of Nomenclature for algae, fungi, and plants allows the 'phyton' part of a genus name optionally to be omitted before '-ophyta', '-ophytina' and '-opsida'.^[4]

The group has also since been treated as a division under the name Trimerophyta^[5] or Trimerophytophyta, as a class under the name Trimeropsida or Trimerophytopsida (as here),^[6] and as an order under the name Trimerophytales.^[7]

Subphylum †Trimerophytina Banks 1975^[8]^[9]
- Class †Trimerophytopsida Foster & Gifford 1974 [Trimeropsida Banks 1975; Psilophytopsida Kidston & Lang 1917; Psilophytidae Nemejc 1963]
  - Order †Trimerophytales Banks ex Kasper et al. 1974 [Psilophytales Pia 1924]
    - Family †Trimerophytaceae Banks 1967 [Psilophytaceae Hirmer 1927; Hostinellaceae Pia 1924; Dawsonitaceae Nemejc 1963]
      - Genus †Dawsonites Nemejc 1963
      - Genus †Hostinella Barrande ex Stur 1882
      - Genus †Oocampsa Andrews, Gensel & Kasper 1975
      - Genus †Euphyllophyton Hao & Beck
      - Genus †Pauthecophyton Xue et al. 2012
      - Genus †Psilophyton Dawson 1859 emend. Hueber & Banks 1967
      - Genus †Trimerophyton Hopping 1956

References

^ Crane, P.R.; Herendeen, P. & Friis, E.M. (2004), "Fossils and plant phylogeny", American Journal of Botany, 91 (10): 1683–99, doi:10.3732/ajb.91.10.1683, PMID 21652317
^ Banks, H.P. (1968), "The early history of land plants", in Drake, E.T. (ed.), Evolution and Environment: A Symposium Presented on the Occasion of the 100th Anniversary of the Foundation of Peabody Museum of Natural History at Yale University, New Haven, Conn.: Yale University Press, pp. 73–107, cited in Banks, H.P. (1980), "The role of Psilophyton in the evolution of vascular plants", Review of Palaeobotany and Palynology, 29: 165–176, doi:10.1016/0034-6667(80)90056-1
^ Banks, H.P. (1975), "Reclassification of Psilophyta", Taxon, 24 (4): 401–413, doi:10.2307/1219491, JSTOR 1219491
^ McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012), International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011, vol. Regnum Vegetabile 154 (electronic ed.), Vienna: A.R.G. Gantner Verlag KG, retrieved 2014-07-02, Article 16.4
^ Taylor, T.N.; Taylor, E.L. & Krings, M. (2009), Paleobotany, The Biology and Evolution of Fossil Plants (2nd ed.), Amsterdam; Boston: Academic Press, ISBN 978-0-12-373972-8, p. 227
^ See, e.g., Berry, C.M. & Fairon-Demaret, M. "The Middle Devonian Flora Revisited". In Gensel & Edwards (2001), pp. 120–139.
^ Banks, H.P. (1970), Evolution and Plants of the Past, London: Macmillan Press, ISBN 978-0-333-14634-7, p. 57
^ Novíkov & Barabaš-Krasni (2015). Modern plant systematics. Liga-Pres. p. 685. doi:10.13140/RG.2.1.4745.6164. ISBN 978-966-397-276-3.
^ "Part 2- Plantae (starting with Chlorophycota)". Collection of genus-group names in a systematic arrangement. Archived from the original on 16 August 2018. Retrieved 30 June 2016.

Bibliography

Gensel, P.G. & Edwards, D., eds. (2001), Plants invade the Land : Evolutionary & Environmental Perspectives, New York: Columbia University Press, ISBN 978-0-231-11161-4